fix: Build Docker image, fix SelectItem empty values, add admin seed script

- Add placeholder env vars for Supabase, Stripe, and Resend in Dockerfile
- Fix empty SelectItem values in POS and payroll forms
- Fix missing Supabase env variables in stats route
- Create seed-admin-users.sql script for Frida Lara, América de la Cruz, and Alejandra Ponce as admin users
- Docker image marcogll/anchoros:test built and pushed successfully

Dockerfile

@@ -19,6 +19,11 @@ COPY . .
 # Variables de entorno para build
 ENV NEXT_TELEMETRY_DISABLED 1
 ENV NODE_ENV production
+ENV NEXT_PUBLIC_SUPABASE_URL=https://placeholder.supabase.co
+ENV NEXT_PUBLIC_SUPABASE_ANON_KEY=placeholder-anon-key
+ENV SUPABASE_SERVICE_ROLE_KEY=placeholder-service-role-key
+ENV STRIPE_SECRET_KEY=sk_test_placeholder_key
+ENV RESEND_API_KEY=re_placeholder_key
 
 # Build optimizado
 RUN npm run build